Physiological sensor system with automatic authentication and validation by means of a radio frequency identification protocol with an integrated RFID interrogator system

ABSTRACT

This invention relates to a physiological sensor which acquires pre-programmed data from an electrode or an electrode array using Radio Frequency Identification (RFID) technology. The source of the sensor may be authenticated by means of a wireless interface between an RFID transponder affixed to the electrode array, and an RFID interrogator embedded in the patient interface cable. The criteria for use are then verified to ensure that they are met by the electrode array before beginning signal acquisition. If the criteria are not met, a message is provided to the user via the monitor.

CROSS-REFERENCE SECTION

This application is a continuation of U.S. patent application Ser. No.13/867,007, filed Apr. 19, 2013, which is a continuation of U.S. patentapplication Ser. No. 13/315,486, filed Dec. 9, 2011, (now U.S. Pat. No.8,427,321), which is a continuation of U.S. patent application Ser. No.11/871,585, filed Oct. 12, 2007, (now U.S. Pat. No. 8,077,039), whichclaims priority to U.S. Provisional Application No. 60/851,437, filedOct. 13, 2006, all of which are incorporated herein by reference intheir entireties.

BACKGROUND OF THE INVENTION

RFID technology-based wireless transmission of data enables effectivecommunication of data and data management in the absence of physicalconnections, with a transmission quality that is equal to contact-basedtechnologies. One such application is the use of RFID technology as analternate to contact smart cards, or other memory devices that requirecontact in order to communicate their stored data.

When acquiring physiological signals for recording and analysis viabiomedical sensors, it is valuable to the user that certain informationabout the sensor be available to the monitoring system. This informationmay include type of sensor, configuration of electrodes, the number oftimes the sensor has been used, date of manufacture of the sensor,identity of the manufacturer and the manufacturing lot number. Themonitor can utilize this information to determine how to process data oreven to detect whether to allow use or to limit reuse of the sensor. Analternative to entering the data manually is to include such data in amemory device integrated into the sensor itself. Integration of memorydevices in biomedical sensors and in medical devices in general has beendocumented in conjunction with numerous previous inventions. Perhaps themost representative is U.S. Pat. No. 6,298,255. In U.S. Pat. No.6,298,255 Cordero et al. describe a sensor system including a monitor, asmart sensor and the accompanying hardware and software interface toauthenticate the source and validity of the sensor. A smart card memorymodule is incorporated into an electrophysiological sensor for thepurpose of storing data pertaining to the sensor. The memory module ismounted on a rigid connector used to connect the sensor to the monitor.Although the data contained in the memory device for the presentinvention may be the same as that described in U.S. Pat. No. 6,298,255,the nature of the memory device and the method by which the systemcommunicates with the memory device are distinct.

In U.S. Patent Application 2004/0008123A1 Carrender et al. focuses onthe use of RFID for monitoring and tracking medical devices utilizingRFID techniques. An RFID tag programmed with information about themanufacturing of the device as well as the status of the device, isattached to the medical device to be monitored. A detection system iscoupled to the tag in order to access the data. In an alternatearrangement the data can be read and revised by a reader device whichmay be linked to a database.

U.S. Patent Application US2005/025842A1 Zarembo describes a system and amethod for managing information related to implantable medical devices.The system is comprises a disposable RFID unit external to theimplantable medical device (IMD) yet packaged with the device. The RFIDunit contains information primarily related to the manufacturing of thedevice. Such data may include inventory information, assembly managementinformation, measurement results, and traceability information. An RFcommunication device is used to interrogate the RFID unit. This RFcommunication device may be associated with the IMD programmer or it maybe part of a global or hospital communication network.

One further RFID application in the medical field is protection againstcounterfeiting of pharmaceutical and medical devices. In U.S. PatentApplication US 2005/0289083 Ngai et al. detail a system that employs aparent-child relationship between two RFID tags for the purpose ofauthenticating products that are delivered in a plurality of containerspackaged within a single package. Each container is affixed with an RFIDchild tag and the outer package is affixed with a parent tag. Usingvarious methodologies based on the data stored in each tag (e.g. a UID)and on information in a database, the authenticity of the relationshipand that authenticity of the package is determined.

SUMMARY OF THE INVENTION

The invention relates to the use of a wireless communication technology,namely RFID, to enable the task of authentication and validation of anelectrode array by a sensing patient interface cable. It also comprisesthe means by which an electrode, electrode array or physiologicalmeasuring device, bearing a passive RFID transponder, or tag, may bedetected and may provide stored data to a RFID interrogator and then toan associated physiological monitoring system. The data may include themanufacturer, information about the manufacturing history and the usehistory of the electrode array for the purposes of authenticating theelectrode array source and verifying that the electrode array meets thecriteria for use (e.g. before expiration date, number of previous uses,etc.). Data that relate to calibration may also be programmed.

This function is performed with the components of the interrogatorsystem, including an interrogator integrated circuit (IC),microprocessor, antenna and antenna matching circuits located within aflexible patient interface cable that connects the electrode array tothe monitoring system. The entire system also performs this functionwith limited power consumption in order to be retrofittable to anexisting non-RFID-based sensor-to-monitor interface. The invention ofthe current application is designed to be compatible with monitoringsystems using the smart memory device-based system of the type shown inU.S. Pat. No. 6,298,255. Therefore, it must meet all the requirements ofthe device described in that patent including power consumption limitsand output data structure as the data is expected in smart memory moduleformat, ISO 7816. When the sensor is used to acquire signals, i.e. whenthe patient interface cable and the electrode array are mated throughconnection of the snaps to the snap sockets, the pair of RFID antennaehas no more than 15 mm of separation. This read distance is shorter thantypical application. Consequently, the power consumption can be reducedand the reliability is increased. However additional measures in theinterrogator system circuitry are required to further control and limitthe power consumption.

Electrophysiological data is transmitted from the contact surface orsurfaces of the electrode(s) to the physiological monitor by directcontact between conductive snaps on the electrode array and snap socketsembedded in the patient interface cable. When the snaps are mated thetransponder which is located on the sensor is detected. In thisinvention, there is no need for a network of RFID interrogatorlocations, or even the need to carry around a handheld interrogator dueto the fact that the interrogator is integrated into a cable systemwhich would otherwise be required to transmit the electrophysiologicalsignal to the biopotential monitor.

When the electrode array with its affixed transponder is brought withinthe field generated by the interrogator, there is a measurable voltagechange. This voltage change can be used as a means to detect thepresence of the transponder. The presence of the transponder may also beidentified by successful interrogation and response of the transponder.Once the transponder is detected, the two components can communicate viamodulation of the RF electric field generated by the antennae.

Upon detection of the RFID transponder, the interrogator prompts thetransponder IC for its stored data. The data is then converted by themicroprocessor, to the memory format in ISO7816 that is expected by thelegacy monitoring system. In an alternate embodiment, the data may firstneed to be decrypted prior to conversion as an added element ofsecurity. The information is then processed as described in U.S. Pat.No. 6,298,255.

In a hospital setting, this physiological sensor may frequently be usedin the presence of electrosurgical units which are potentially asignificant source of interference in the communication between theinterrogator and the transponder. Therefore extra measures are taken inthis sensor design to reduce interference from electrosurgical units(ESU) which are frequently encountered in a hospital setting. Todecrease ESU interference, filtering is added to the patient interfacecable.

This implementation of wireless technology may be further advantageousin a context in which a physiological sensor does not form a mechanicalconnection with the monitor but rather the acquired signals are alsotransmitted by a wireless technology.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a block diagram illustrating the components of theElectrophysiological Sensor System

FIG. 2 a is a perspective view of a multi-electrode embodiment of anelectrode array with a mounted RFID transponder.

FIG. 2 b is a perspective view of a single-electrode embodiment of anelectrode array with a mounted RFID transponder.

FIG. 3 is a drawing of a sample RFID transponder for this application(HF)

FIG. 4 a is a side view of the complete patient interface cable and itsrelationship to the biomedical sensor for electrophysiological signalacquisition.

FIG. 4 b is a top view of an unmolded patient interface cable showingthe wiring and integrated hardware.

FIG. 5 is a block diagram of the relationship between the interrogatorand the transponder.

FIG. 6 is a flow chart of the detection and communication during theinterrogation process.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS:

The invention consists of an electrophysiological sensor 1 (FIG. 1),comprised of an electrode array 3 used for acquiring physiologicalsignals from a patient and an interface cable 2 which connects to theelectrode array 3. This sensor is typically connected to a biopotentialsignal monitor 7 that contains memory storage 4, a processor 5 and adisplay device 6 which are used to store, analyze and display thephysiological signals to a user.

Electrophysiological data is transmitted from the contact surface orsurfaces of the electrode 10 or electrodes (shown in FIGS. 2 a & 2 b) tothe monitor 7 (not shown) by the typical method of direct contactbetween conductive snaps 11 on the electrode array and snap sockets 30(referring to the top half of a snap connector) embedded in theinterface cable. The electrode array, which adheres to the patient'sskin consists of at least one electrophysiological electrode 10,preferably constructed of silver/silver chloride. An RFID transponder 12is adhesively affixed to the electrode array.

An RFID transponder 12 is comprised of an antenna 21 and a transponderintegrated circuit (IC) 22 (FIG. 3). The microchip 22 on the RFIDtransponder 12 is a memory device that is programmed by the biomedicalsensor manufacturer with data regarding the history and status of theelectrode array. In this embodiment, the RFID transponder 12 isconstructed on a flexible substrate 23, preferably polyester orpolypropylene. It has a coil antenna 21 preferably formed of etched ordeposited copper, but may also be aluminum. The RFID transponder IC 22has adequate EEPROM memory capacity of to store any required data.Alternately, the memory may be EPROM or PROM (programmable read-onlymemory). Preferably the transponder IC 22 has a memory capacity of256-512 bytes. One such IC is the NXP SLIS3001 (I-CODE1)(NXPSemiconductors Netherlands B.V., Eindhoven, The Netherlands). The RFIDtransponder 12 is passive which means that it contains no battery anddraws its power from the host system via the interrogator antenna (notshown). The transponder resonates in the High Frequency (HF) band(˜13.56 MHz)

The transponder 12 has adhesive backing and is formed in the shape of anannular ring, no more than 1.5 inches (38 mm) in diameter. This is inline with commercially available RFID transponders. The transponder isaffixed to the electrode array with the antenna and the IC on thesurface that contacts the electrode, thus aiding in protecting theelectronics from damage due to exposure to liquid or improper handling.It is positioned around a male EKG electrode-type post or “snap” 11 onone electrode in the array. In alternate embodiments, the transpondercould be of any shape or design that would enable it to be mounted onthe electrode array. In an alternate embodiment still, multipletransponders may be placed on multiple electrodes in the array.

Upon connection of the electrode array 3 to the patient interface cable2, both electrophysiological data and data relating to the electrodearray are transmitted to the biopotential signal monitor (not shown).Electrophysiological data is transmitted via the snaps while electrodearray data stored on the transponder IC such as data pertaining toauthentication, manufacturing information and validity of the electrodearray, are transmitted by radio frequency transmission (RF).

The patient interface cable 2 (FIGS. 4 a & 4 b) has a connector 39 atone end that mates with the biopotential signal monitor. At the opposingend, the cable has multiple embedded EKG electrode-type sockets 30designed to attach to the snap in the center of each electrode in theelectrode array. There are an equivalent number of sockets in the cableas there are electrodes in the array. There may be as few as one socketin the cable. The EKG electrode-type sockets 30 are electricallyconnected by a series of conductive wires 31. In an alternate embodimentthe sockets are mounted in fixed positions in a flexible circuit boardwith conductive traces to from the cable and to conduct signal from eachelectrode of the array via the snap socket to the monitor. In yetanother embodiment the transmission lines are conductive traces whichare constructed of a conductive ink, such as silver/silver chloride(Ag/AgCl) printed on a flexible substrate on the substrate of theflexible circuit board.

The patient interface cable housing the EKG electrode-type sockets andconductive transmission lines is over-molded 38 with a thermoplasticelastomeric material. Only the bottom surface of the snap socket isexposed for attachment to the electrode array 3. This assists inprotecting the circuit and the contacts from the harsh environment of anoperating room, reduces the likelihood of liquid ingress and alsocreates a flexible interface for easy use by clinicians and for patientfit.

The patient interface cable 2 also houses an RFID interrogator system.The interrogator system is comprised of an interrogator IC, the antennafor the interrogator 32, and 2 matching circuits. The interrogator ICmay have an integrated microprocessor for preliminary processing of thedata.

In the preferred embodiment, the interrogator system is contained on twoprinted circuit boards (PCBs) embedded in the cable—the Tail PCB 40 andthe Head PCB 33. The interrogator IC may be the MLX90121 (Melexis) chipor a similar commercially available chip that operates in the HFfrequency band (13.56 MHz). The RFID interrogator IC may be capable ofcommunicating with microchips compliant with any of various ISOcontactless integrated circuit proximity and vicinity card protocols,e.g. ISO 14443A/B, ISO 15693.

In this embodiment, the interrogator antenna is located on the Head PCB33 while the interrogator IC is located on the Tail PCB 40. Componentsfor power management and to reduce interference may also be mounted onthis Tail PCB 40. Additionally, the Tail PCB may also contain arelatively narrow band passive filter centered around 13.56 MHz toreceive the input of the MLX90121, or equivalent interrogator IC. Theexternal filter keeps the ESU interference from exceeding the inputvoltage capacity of the MLX90121.

For power management, in the preferred embodiment, a switching powersupply is used to limit the voltage to the Power Amplifier of theMLX90121 rather than a standard current limiting circuit which usespower less efficiently. In another embodiment, the power limitation isovercome by using a bank of capacitors on the Tail PCB. Capacitors canbe charged at a slow rate and draw the charge out of them at a highrate. A 10 mF capacitor bank can be charged up to 5 volts with a 1 macharge current over a period of 1 second and then it can be drawn at 10ma for 0.1 second.

In this preferred embodiment, the interrogator antenna 32 is etched onthe Head PCB 33. Two conductive wires, specified as a 100 ohm twistedpair 34 are connected at one end to the Head PCB 33 and at the otherend, to the Tail PCB 40. Such conductive wires transmit AC signal to theHead PCB thus providing power to the interrogator antenna 32. Asillustrated in FIG. 5, attached to the interrogator IC 50 is animpedance matching circuit 51 that matches the output impedance of theinterrogator IC 50 to the 100 ohm twisted pair transmission line 34.Transmission lines of other impedances (e.g. 50 ohm or 300 ohm) may alsobe used. At the far end of the transmission line is a matching circuit52 and an antenna 32. The matching circuit 52 matches the impedance ofthe transmission line 34 to the impedance of the antenna 32 and forms aresonant circuit with the antenna. This matching circuit may alsoinclude a resistor to lower the Q of the resonant circuit to increasethe bandwidth of the circuit. The interrogator antenna 32 generates anRF electric field with the transponder antenna 21 enabling communicationwith the transponder IC 22.

The placement of this Head PCB 33 is around or alternately beside a snapsocket in the location corresponding to the affixed transponder on theelectrode array. The Head PCB is held in place by a solder connection tothe snap. Alternately it may be held in place by a thermoplasticover-mold (or pre-mold). The Head PCB may share the same flexiblesubstrate as the conductive traces and/or may be a combination of aflexible and a rigid circuit board to increase strength and reliability.The interrogator antenna 32 has a maximum diameter of 30 mm. Theinterrogator antenna 32 on the Head PCB 33 is placed such that when thecable and electrode array are mated, the antenna is positioned directlyabove and parallel to the RFID transponder 12 affixed to the electrodearray, as illustrated in FIG. 4 a. In the preferred embodiment, the tailPCB 40 is integrated into the connector 39 that mates with thebiopotential signal monitor.

In one embodiment, the interrogator antenna and interrogator IC areco-located on the Head PCB. The matching circuits are then modified toaccommodate the change in relative position between the interrogatorantenna and the interrogator IC. In yet another embodiment, the Tail PCB40 containing the circuitry including an interrogator IC, amicroprocessor, and electronics and for matching the interrogatorantenna may be housed in an independent enclosure or be integrated intothe monitor hardware.

In this application, when the electrode array 3 is mechanically attachedto the patient interface cable 2, by the conductive snaps 11 mated tosnap sockets 30, and the interrogator antenna 32 and the RFIDtransponder 12 are consequently in proximity to the other, the preferreddistance between the interrogator antenna and the transponder when thecable is connected to the electrode array is 2-15 mm.

When the transponder IC is brought within the field generated by theinterrogator, a measurable voltage change is observed at the output ofthe antenna matching circuit 52. Detection of this voltage change isused as a means to detect the presence of the transponder. In oneembodiment, the interrogator system continuously checks via continuouspolling for a change in voltage by way of an analog-to-digital converterthat is constantly sampling the voltage. An alternate embodiment woulduse a hardware voltage comparator to sense the change in voltage. Thisvoltage change can be used as a means to detect the presence of thetransponder. An alternate means of transponder detection is to simplyinterrogate the device and determine if there is any response.

These detection methods also enable the interrogator system to detectthe absence, or removal of the transponder from the detection field.Thus, the biopotential monitoring system knows when the electrode arrayis and is not connected to the patient interface cable. Once thetransponder is detected, the two components can communicate via RFmodulation as per standard RFID communication methods.

FIG. 6 outlines the high-level steps for detection and communication.The system detects a change in voltage 60 and then proceeds tointerrogate the transponder IC 61. If the transponder does not respondto interrogation by the interrogator 62, the state of the system returnsback to trying to detect a voltage change 60. If the transponder doesrespond to interrogation by the interrogator 63, the interrogatorproceeds to read the data packet stored on the transponder IC 64contained by the transponder. Then the data packet is decrypted by themicroprocessor if the data was previously encrypted 65 and the structureof the data is converted to ISO7816 format to emulate a smart module 66,which is what is expected by the legacy host system. Once the data isconverted, it is passed on to the biopotential signal monitor forfurther processing 67—primarily authentication and validation of thesensor. The authentication and validation aspects of this system aredescribed in detail in U.S. Pat. No. 6,298,255. Additionally, the datapacket may be revised, possibly to reflect a change in sensor status,for example incrementing a usage counter, and then written to thetransponder IC.

Various data concerning the origin and manufacture of the electrodearray are stored in the transponder IC. This data includes but is notlimited to a key code, a manufacturer code, an OEM code, a product shelflife code, an electrode type code, the lot code and serial number andthe usage count. All or a part of the data are stored in encrypted formwith a single or multiple layered encryption. The data may also includea digital signature that may be used to authenticate and validate theelectrode array in the manner taught by U.S. Pat. No. 6,298,255. Themanufacturer code is used to authenticate the source of the electrodearray, while the product shelf-life code, the usage count and the sensortype code are used to determine whether the sensor meets the necessarycriteria for use. Calibration data relating to the electrode array mayalso be stored in the transponder IC, allowing avoidance ofrecalibration if the sensor is disconnected and reconnected to adifferent monitor. This is commonly done in medical or hospital settingsin conjunction with patient transport.

In an alternate embodiment, where the restrictions imposed by the legacysystem are not applied, methods and components relating to the powerlimiting circuitry and to the conversion of the data to contact basedISO7816 data structure are not incorporated.

In an alternative embodiment, the RFID transponder is embedded into anoptoelectrical device for obtaining biological signals. These devicescontain no direct contact with the patient, so the RFID transponder is aconvenient way to keep the device from having any external contacts suchas the ones on a contact smart chip.

The incorporation of RFID-based technology into an electrophysiologicalmonitoring system provides several important and significant advantages,both technical and economic. The wide-spread and ever increasingacceptance and demand for RFID tagging (i.e. affixing an RFIDtransponder on any item) in a number of industries has driven the costof RFID microchips to much less than that of non-RFID semiconductormemory devices of similar capability and capacity. In addition,implementing RFID as an alternative to contact smart chips requiresfewer electrical connections to the sensor. This provides a lowermanufacturing cost due to the reduction in the required number ofconductive traces and contact pads on both the sensor side and themonitor side of their connection. The lack of contact connections andthe absence of the associated connection pads and conductors alsoprovide increased reliability by avoiding device failures caused by poorcontact impedances and the likelihood of a communication malfunction dueto the ingress of fluids such as water or body fluids into the spacebetween adjacent contact pads. This implementation of wirelesstechnology may also be advantageous in a context in which the biomedicalsensor does not form a mechanical connection with the monitor but ratherthe acquired signals are also transmitted by a wireless technology. Insuch a context, this invention has important advantages for maintainingdevice sterility.

While the foregoing invention has been described with reference to itspreferred embodiments, various alterations and modifications will occurto those skilled in the art. All such alterations and modifications areintended to fall within the scope of the appended claims.

What is claimed is:
 1. A physiological sensor for communicatinginformation to a medical monitor, comprising: sensor structureconfigured to pass a physiological output from a subject to the medicalmonitor; and an RFID transponder configured to transmitnon-physiological information to the medical monitor by a wirelesstransmission technique.
 2. The physiological sensor of claim 1, whereinthe RFID transponder comprises an antenna and transponder circuitry. 3.The physiological sensor of claim 1, wherein the antenna comprises acoil antenna.
 4. The physiological sensor of claim 3, wherein thediameter of the coil antenna is no more than 38 mm.
 5. The physiologicalsensor of claim 1, wherein the RFID transponder comprises a memorydevice.
 6. The physiological sensor of claim 5, wherein the memorydevice is programmed with the non-physiological information.
 7. Thephysiological sensor of claim 5, wherein the memory device is programmedwith one or more of a key code, a manufacturer code, calibration data,an OEM code, a product shelf life code, a sensor type code, a lot code,a serial number, and usage count.
 8. The physiological sensor of claim5, wherein the memory device is programmed with a digital signature forauthentication and validation.
 9. The physiological sensor of claim 1,wherein the RFID transponder is configured to transmit thenon-physiological information in response to an interrogation from anRFID interrogator.
 10. The physiological sensor of claim 1, wherein theRFID transponder comprises an antenna and wherein the RFID transponderis a passive device that draws power from the antenna.
 11. Thephysiological sensor of claim 1, wherein the physiological output is aphysiological signal
 12. The physiological sensor of claim 1, whereinthe sensor structure comprises an electrode.
 13. The physiologicalsensor of claim 1, wherein the sensor structure comprises anoptoelectrical device.
 14. The physiological sensor of claim 1, furthercomprising an interface cable.
 15. The physiological sensor of claim 14,further comprising a mating receptacle configured to connect theinterface cable to the medical monitor.
 16. The physiological sensor ofclaim 15, wherein the RFID transponder is located within the matingreceptacle.
 17. A physiological monitoring system, comprising: aphysiological monitor comprising: an RFID interrogator; and an RFIDantenna; and a sensor comprising: sensor structure configured to pass aphysiological output from a subject to the physiological monitor; and anRFID transponder configured to transmit non-physiological information tothe physiological monitor by a wireless transmission technique.
 18. Thephysiological monitoring system of claim 17, wherein the RFIDtransponder is configured to transmit the non-physiological informationin response to an interrogation from the RFID interrogator.
 19. Thephysiological monitoring system of claim 17, wherein the RFIDtransponder comprises an antenna and transponder circuitry.
 20. Thephysiological monitoring system of claim 17, wherein the sensor furthercomprises: an interface cable; and a mating receptacle configured toconnect the interface cable to the medical monitor.
 21. Thephysiological monitoring system of claim 17, wherein the RFIDtransponder comprises an antenna and wherein the RFID transponder is apassive device that draws power from the antenna.